This invention relates to impacting crushers. Non-limiting examples include one way and reversible hammermills, in-out machines, over and out machines, ring type granulators, impactors and other machines with and without grates, breaker blocks, cage bars and the like surrounding the rotor. In general, such machines are designed to shatter hard and/or abrasive mineral material such as metal ores, coal, stone and glass. Shattering is caused at least in part and to a substantial extent by high energy collision between the material and angularly spaced rotating impact members, such as hammers, rings, bars, paddles or other striking members. These extend outwardly from a rotating shaft mounted for rotation in a surrounding housing provided with a feed inlet and a reduced material discharge outlet. When fully extended by centrifugal force, the peripheries of the impact members travel in what is referred to as a "hammer circle".
The high levels of kinetic energy produced in such machines and the hardness and abrasiveness of the feed materials tend to abrasively wear away those portions of the impact member surfaces which are involved in the collisions. Such wear tends to degrade machine performance, with some machines varying from others in the extent and manner in which they are affected by such wear. Eventually, wearing of the impact members proceeds to the point where compensating adjustment, overhaul or parts replacement becomes necessary.
Impacting crushers are generally employed in high tonnage continuous operations in which the machines are fed by conveyors, such as for example conveyor belts, drag link conveyors, screw conveyors, vibrating conveyors and others. Conveyor cost factors and impacting crusher capacity considerations have generally resulted in relatively narrow conveyors being used to feed machines with relatively wide rotors. Assume that one's object is to select a combination of conveyor and impacting crusher capable of conveying stone, coal or the like over an extended distance and then crushing it with minimum capital investment. Conveyor capital costs can be held to a minimum by employing a conveyor of minimum width relative to the required through-put capacity. However, the state of the art of impacting crusher design being what it is, it has generally been considered necessary that the rotor be several times wider than the width of the conveyor, e.g. 3-4 times wider, in order to handle capacity through-put from the conveyor without choking. Because of these and other factors, there are in existence today many installations using impacting crushers with relatively wide rotors which are fed by relatively narrow conveyors.
Such installations are subject to a number of problems which have been evident for many years. Assuming that a narrow width discharge from a conveyor belt is directed to the center of a relatively wide rotor, the central portion of the rotor sustains more wear per unit of oeprating time than its side portions. Thus, for instance, if the impacting crusher is a hammermill having a plurality of groups of hammers arranged side by side along the axis of the rotor, the center groups of hammers may be worn excessively when the hammers in the side groups are still serviceable. Had such uneven wear not occurred, the machine could have operated for a longer interval and still maintained desired product size. On the other hand, if the impacting crusher is of a type which requires a certain critical clearance between the hammer circle and an adjustable surrounding cage, it may not be possible to fully utilize the wearing capabilities of the central portion of the rotor; the differences between the diameter of the central portion and less worn side portions of the rotor may be sufficient so that when the cage is adjusted for proper clearance relative to the central portion of the rotor, there may be inadequate clearance or even interference between the cage and the side portions of the rotor.
Another known problem relates to the matter of where and in what direction the feed material penetrates the circle described by the periphery of the rotor, i.e. the hammer circle. A given design of impacting crushers ordinarily has an optimum penetration location. For example, the optimum area of penetration is generally top dead center in a reversible machine. In hammermills with sloping breaker plates, the optimum area is often the "pinch point", the location where the impact members approach closest to the breaker plate. The extent to which feed material penetration deviates from the desired location can produce safety and maintenance problems. For example, in machines wherein the pinch point is the optimum penetration location, material not entering at the pinch point can cause ricocheting, sometimes referred to as "foul balling", with heavy chunks of material being thrown back up into the feed connection chutes between the crusher housing and the conveyor. This can be both damaging and dangerous. This same difficulty is promoted if the feed enters at the optimum location but in varying directions. Thus, vertical penetration is preferred.
A troughed belt is the type of conveyor most commonly used to feed impacting crushers. Such belt/crusher installations are usually designed in a manner such that the feed materials depart the belt on a longitudinally spreading trajectory of narrow width with both horizontal and vertical components of motion. Special guide chutes have been used in some cases to limit the horizontal motion and/or longitudinal spread of the conveyor discharge. However, certain of these designs cause significant bouncing of the feed material back and forth between the interior walls pg,5 of the chute, so that fewer particles enter the hammer circle on the desired vertical path.
Another problem is the matter of the speed at which the feed material penetrates the hammer circle. In a given machine, operating at a given rotor speed, there will be an optimum speed at which the feed material should penetrate the hammer circle for most effective size reduction and through-put. The speed of penetration of the feed generally depends on the height from which it drops from the conveyor to the hammer circle. The above-described special delivery chutes for confining longitudinal spread of the conveyor discharge complicate the attainment of the desired penetration speed. When sufficiently effective in stream confinement, they can exert sufficient friction on the feed to significantly alter its penetration speed, in some cases resulting in less than adequate speed of penetration. Thus, it has been a problem in the art to obtain in combination even wear across the rotor, along with optimum location, direction and speed of penetration into the hammer circle.
Impacting crushers have been in use for over half a century and have been fed improperly by relatively narrow conveyors for most of that period. For dozens of years persons skilled in the art have observed the problems described above and the extra costs arising from these problems. Various attempts have been made to design serviceable distributing devices for distributing feed material more evenly to impacting crushers. However, such designs have not achieved widespread acceptance as a solution to the problem, as evidenced by the fact that there are many installations in existence which are being operated without any feed distributor whatsoever, and in which the operators continue to tolerate the extra maintenance and expense of uneven rotor wear. Moreover, new installations are being made which are subject to the same problems. Accordingly, it appears that there is a continuing need for improved impacting crushers with feed distributors capable of maintaining even distribution of wear across the rotor.